/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 * <p>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p>
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.hadoop.hdfs.protocol;

import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.EnumSet;
import java.util.List;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.crypto.CryptoProtocolVersion;
import org.apache.hadoop.fs.BatchedRemoteIterator.BatchedEntries;
import org.apache.hadoop.fs.CacheFlag;
import org.apache.hadoop.fs.ContentSummary;
import org.apache.hadoop.fs.CreateFlag;
import org.apache.hadoop.fs.FileAlreadyExistsException;
import org.apache.hadoop.fs.FsServerDefaults;
import org.apache.hadoop.fs.InvalidPathException;
import org.apache.hadoop.fs.Options;
import org.apache.hadoop.fs.Options.Rename;
import org.apache.hadoop.fs.ParentNotDirectoryException;
import org.apache.hadoop.fs.UnresolvedLinkException;
import org.apache.hadoop.fs.XAttr;
import org.apache.hadoop.fs.XAttrSetFlag;
import org.apache.hadoop.fs.permission.AclEntry;
import org.apache.hadoop.fs.permission.AclStatus;
import org.apache.hadoop.fs.permission.FsAction;
import org.apache.hadoop.fs.permission.FsPermission;
import org.apache.hadoop.hdfs.DFSConfigKeys;
import org.apache.hadoop.hdfs.inotify.EventBatchList;
import org.apache.hadoop.hdfs.protocol.HdfsConstants.RollingUpgradeAction;
import org.apache.hadoop.hdfs.security.token.block.DataEncryptionKey;
import org.apache.hadoop.hdfs.security.token.delegation.DelegationTokenIdentifier;
import org.apache.hadoop.hdfs.security.token.delegation.DelegationTokenSelector;
import org.apache.hadoop.hdfs.server.namenode.NotReplicatedYetException;
import org.apache.hadoop.hdfs.server.namenode.SafeModeException;
import org.apache.hadoop.hdfs.server.protocol.DatanodeStorageReport;
import org.apache.hadoop.io.EnumSetWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.retry.AtMostOnce;
import org.apache.hadoop.io.retry.Idempotent;
import org.apache.hadoop.security.AccessControlException;
import org.apache.hadoop.security.KerberosInfo;
import org.apache.hadoop.security.token.Token;
import org.apache.hadoop.security.token.TokenInfo;

/**********************************************************************
 * ClientProtocol is used by user code via 
 * {@link org.apache.hadoop.hdfs.DistributedFileSystem} class to communicate 
 * with the NameNode.  User code can manipulate the directory namespace, 
 * as well as open/close file streams, etc.
 *
 **********************************************************************/
@InterfaceAudience.Private
@InterfaceStability.Evolving
@KerberosInfo(
        serverPrincipal = DFSConfigKeys.DFS_NAMENODE_KERBEROS_PRINCIPAL_KEY)
@TokenInfo(DelegationTokenSelector.class)
public interface ClientProtocol {

    /**
     * Until version 69, this class ClientProtocol served as both
     * the client interface to the NN AND the RPC protocol used to
     * communicate with the NN.
     *
     * This class is used by both the DFSClient and the
     * NN server side to insulate from the protocol serialization.
     *
     * If you are adding/changing this interface then you need to
     * change both this class and ALSO related protocol buffer
     * wire protocol definition in ClientNamenodeProtocol.proto.
     *
     * For more details on protocol buffer wire protocol, please see
     * .../org/apache/hadoop/hdfs/protocolPB/overview.html
     *
     * The log of historical changes can be retrieved from the svn).
     * 69: Eliminate overloaded method names.
     *
     * 69L is the last version id when this class was used for protocols
     *  serialization. DO not update this version any further.
     */
    public static final long versionID = 69L;

    ///////////////////////////////////////
    // File contents
    ///////////////////////////////////////

    /**
     * Get locations of the blocks of the specified file within the specified range.
     * DataNode locations for each block are sorted by
     * the proximity to the client.
     * <p>
     * Return {@link LocatedBlocks} which contains
     * file length, blocks and their locations.
     * DataNode locations for each block are sorted by
     * the distance to the client's address.
     * <p>
     * The client will then have to contact
     * one of the indicated DataNodes to obtain the actual data.
     *
     * @param src file name
     * @param offset range start offset
     * @param length range length
     *
     * @return file length and array of blocks with their locations
     *
     * @throws AccessControlException If access is denied
     * @throws FileNotFoundException If file <code>src</code> does not exist
     * @throws UnresolvedLinkException If <code>src</code> contains a symlink
     * @throws IOException If an I/O error occurred
     */
    @Idempotent
    public LocatedBlocks getBlockLocations(String src,
                                           long offset,
                                           long length)
            throws AccessControlException, FileNotFoundException,
            UnresolvedLinkException, IOException;

    /**
     * Get server default values for a number of configuration params.
     * @return a set of server default configuration values
     * @throws IOException
     */
    @Idempotent
    public FsServerDefaults getServerDefaults() throws IOException;

    /**
     * Create a new file entry in the namespace.
     * <p>
     * This will create an empty file specified by the source path.
     * The path should reflect a full path originated at the root.
     * The name-node does not have a notion of "current" directory for a client.
     * <p>
     * Once created, the file is visible and available for read to other clients.
     * Although, other clients cannot {@link #delete(String, boolean)}, re-create or
     * {@link #rename(String, String)} it until the file is completed
     * or explicitly as a result of lease expiration.
     * <p>
     * Blocks have a maximum size.  Clients that intend to create
     * multi-block files must also use
     * {@link #addBlock}
     *
     * @param src path of the file being created.
     * @param masked masked permission.
     * @param clientName name of the current client.
     * @param flag indicates whether the file should be
     * overwritten if it already exists or create if it does not exist or append.
     * @param createParent create missing parent directory if true
     * @param replication block replication factor.
     * @param blockSize maximum block size.
     * @param supportedVersions CryptoProtocolVersions supported by the client
     *
     * @return the status of the created file, it could be null if the server
     *           doesn't support returning the file status
     * @throws AccessControlException If access is denied
     * @throws AlreadyBeingCreatedException if the path does not exist.
     * @throws DSQuotaExceededException If file creation violates disk space
     *           quota restriction
     * @throws FileAlreadyExistsException If file <code>src</code> already exists
     * @throws FileNotFoundException If parent of <code>src</code> does not exist
     *           and <code>createParent</code> is false
     * @throws ParentNotDirectoryException If parent of <code>src</code> is not a
     *           directory.
     * @throws NSQuotaExceededException If file creation violates name space
     *           quota restriction
     * @throws SafeModeException create not allowed in safemode
     * @throws UnresolvedLinkException If <code>src</code> contains a symlink
     * @throws SnapshotAccessControlException if path is in RO snapshot
     * @throws IOException If an I/O error occurred
     *
     * RuntimeExceptions:
     * @throws InvalidPathException Path <code>src</code> is invalid
     * <p>
     * <em>Note that create with {@link CreateFlag#OVERWRITE} is idempotent.</em>
     */
    @AtMostOnce
    public HdfsFileStatus create(String src, FsPermission masked,
                                 String clientName, EnumSetWritable<CreateFlag> flag,
                                 boolean createParent, short replication, long blockSize,
                                 CryptoProtocolVersion[] supportedVersions)
            throws AccessControlException, AlreadyBeingCreatedException,
            DSQuotaExceededException, FileAlreadyExistsException,
            FileNotFoundException, NSQuotaExceededException,
            ParentNotDirectoryException, SafeModeException, UnresolvedLinkException,
            SnapshotAccessControlException, IOException;

    /**
     * Append to the end of the file.
     * @param src path of the file being created.
     * @param clientName name of the current client.
     * @return information about the last partial block if any.
     * @throws AccessControlException if permission to append file is
     * denied by the system. As usually on the client side the exception will
     * be wrapped into {@link org.apache.hadoop.ipc.RemoteException}.
     * Allows appending to an existing file if the server is
     * configured with the parameter dfs.support.append set to true, otherwise
     * throws an IOException.
     *
     * @throws AccessControlException If permission to append to file is denied
     * @throws FileNotFoundException If file <code>src</code> is not found
     * @throws DSQuotaExceededException If append violates disk space quota
     *           restriction
     * @throws SafeModeException append not allowed in safemode
     * @throws UnresolvedLinkException If <code>src</code> contains a symlink
     * @throws SnapshotAccessControlException if path is in RO snapshot
     * @throws IOException If an I/O error occurred.
     *
     * RuntimeExceptions:
     * @throws UnsupportedOperationException if append is not supported
     */
    @AtMostOnce
    public LocatedBlock append(String src, String clientName)
            throws AccessControlException, DSQuotaExceededException,
            FileNotFoundException, SafeModeException, UnresolvedLinkException,
            SnapshotAccessControlException, IOException;

    /**
     * Set replication for an existing file.
     * <p>
     * The NameNode sets replication to the new value and returns.
     * The actual block replication is not expected to be performed during
     * this method call. The blocks will be populated or removed in the
     * background as the result of the routine block maintenance procedures.
     *
     * @param src file name
     * @param replication new replication
     *
     * @return true if successful;
     *         false if file does not exist or is a directory
     *
     * @throws AccessControlException If access is denied
     * @throws DSQuotaExceededException If replication violates disk space
     *           quota restriction
     * @throws FileNotFoundException If file <code>src</code> is not found
     * @throws SafeModeException not allowed in safemode
     * @throws UnresolvedLinkException if <code>src</code> contains a symlink
     * @throws SnapshotAccessControlException if path is in RO snapshot
     * @throws IOException If an I/O error occurred
     */
    @Idempotent
    public boolean setReplication(String src, short replication)
            throws AccessControlException, DSQuotaExceededException,
            FileNotFoundException, SafeModeException, UnresolvedLinkException,
            SnapshotAccessControlException, IOException;

    /**
     * Get all the available block storage policies.
     * @return All the in-use block storage policies currently.
     */
    @Idempotent
    public BlockStoragePolicy[] getStoragePolicies() throws IOException;

    /**
     * Set the storage policy for a file/directory
     * @param src Path of an existing file/directory.
     * @param policyName The name of the storage policy
     * @throws SnapshotAccessControlException If access is denied
     * @throws UnresolvedLinkException if <code>src</code> contains a symlink
     * @throws FileNotFoundException If file/dir <code>src</code> is not found
     * @throws QuotaExceededException If changes violate the quota restriction
     */
    @Idempotent
    public void setStoragePolicy(String src, String policyName)
            throws SnapshotAccessControlException, UnresolvedLinkException,
            FileNotFoundException, QuotaExceededException, IOException;

    /**
     * Set permissions for an existing file/directory.
     *
     * @throws AccessControlException If access is denied
     * @throws FileNotFoundException If file <code>src</code> is not found
     * @throws SafeModeException not allowed in safemode
     * @throws UnresolvedLinkException If <code>src</code> contains a symlink
     * @throws SnapshotAccessControlException if path is in RO snapshot
     * @throws IOException If an I/O error occurred
     */
    @Idempotent
    public void setPermission(String src, FsPermission permission)
            throws AccessControlException, FileNotFoundException, SafeModeException,
            UnresolvedLinkException, SnapshotAccessControlException, IOException;

    /**
     * Set Owner of a path (i.e. a file or a directory).
     * The parameters username and groupname cannot both be null.
     * @param src file path
     * @param username If it is null, the original username remains unchanged.
     * @param groupname If it is null, the original groupname remains unchanged.
     *
     * @throws AccessControlException If access is denied
     * @throws FileNotFoundException If file <code>src</code> is not found
     * @throws SafeModeException not allowed in safemode
     * @throws UnresolvedLinkException If <code>src</code> contains a symlink
     * @throws SnapshotAccessControlException if path is in RO snapshot
     * @throws IOException If an I/O error occurred
     */
    @Idempotent
    public void setOwner(String src, String username, String groupname)
            throws AccessControlException, FileNotFoundException, SafeModeException,
            UnresolvedLinkException, SnapshotAccessControlException, IOException;

    /**
     * The client can give up on a block by calling abandonBlock().
     * The client can then either obtain a new block, or complete or abandon the
     * file.
     * Any partial writes to the block will be discarded.
     *
     * @param b         Block to abandon
     * @param fileId    The id of the file where the block resides.  Older clients
     *                    will pass GRANDFATHER_INODE_ID here.
     * @param src       The path of the file where the block resides.
     * @param holder    Lease holder.
     *
     * @throws AccessControlException If access is denied
     * @throws FileNotFoundException file <code>src</code> is not found
     * @throws UnresolvedLinkException If <code>src</code> contains a symlink
     * @throws IOException If an I/O error occurred
     */
    @Idempotent
    public void abandonBlock(ExtendedBlock b, long fileId,
                             String src, String holder)
            throws AccessControlException, FileNotFoundException,
            UnresolvedLinkException, IOException;

    /**
     * A client that wants to write an additional block to the
     * indicated filename (which must currently be open for writing)
     * should call addBlock().
     *
     * addBlock() allocates a new block and datanodes the block data
     * should be replicated to.
     *
     * addBlock() also commits the previous block by reporting
     * to the name-node the actual generation stamp and the length
     * of the block that the client has transmitted to data-nodes.
     *
     * @param src the file being created
     * @param clientName the name of the client that adds the block
     * @param previous  previous block
     * @param excludeNodes a list of nodes that should not be
     * allocated for the current block
     * @param fileId the id uniquely identifying a file
     * @param favoredNodes the list of nodes where the client wants the blocks.
     *          Nodes are identified by either host name or address.
     *
     * @return LocatedBlock allocated block information.
     *
     * @throws AccessControlException If access is denied
     * @throws FileNotFoundException If file <code>src</code> is not found
     * @throws NotReplicatedYetException previous blocks of the file are not
     *           replicated yet. Blocks cannot be added until replication
     *           completes.
     * @throws SafeModeException create not allowed in safemode
     * @throws UnresolvedLinkException If <code>src</code> contains a symlink
     * @throws IOException If an I/O error occurred
     */
    @Idempotent
    public LocatedBlock addBlock(String src, String clientName,
                                 ExtendedBlock previous, DatanodeInfo[] excludeNodes, long fileId,
                                 String[] favoredNodes)
            throws AccessControlException, FileNotFoundException,
            NotReplicatedYetException, SafeModeException, UnresolvedLinkException,
            IOException;

    /**
     * Get a datanode for an existing pipeline.
     *
     * @param src the file being written
     * @param fileId the ID of the file being written
     * @param blk the block being written
     * @param existings the existing nodes in the pipeline
     * @param excludes the excluded nodes
     * @param numAdditionalNodes number of additional datanodes
     * @param clientName the name of the client
     *
     * @return the located block.
     *
     * @throws AccessControlException If access is denied
     * @throws FileNotFoundException If file <code>src</code> is not found
     * @throws SafeModeException create not allowed in safemode
     * @throws UnresolvedLinkException If <code>src</code> contains a symlink
     * @throws IOException If an I/O error occurred
     */
    @Idempotent
    public LocatedBlock getAdditionalDatanode(final String src,
                                              final long fileId, final ExtendedBlock blk,
                                              final DatanodeInfo[] existings,
                                              final String[] existingStorageIDs,
                                              final DatanodeInfo[] excludes,
                                              final int numAdditionalNodes, final String clientName
    ) throws AccessControlException, FileNotFoundException,
            SafeModeException, UnresolvedLinkException, IOException;

    /**
     * The client is done writing data to the given filename, and would
     * like to complete it.
     *
     * The function returns whether the file has been closed successfully.
     * If the function returns false, the caller should try again.
     *
     * close() also commits the last block of file by reporting
     * to the name-node the actual generation stamp and the length
     * of the block that the client has transmitted to data-nodes.
     *
     * A call to complete() will not return true until all the file's
     * blocks have been replicated the minimum number of times.  Thus,
     * DataNode failures may cause a client to call complete() several
     * times before succeeding.
     *
     * @param src the file being created
     * @param clientName the name of the client that adds the block
     * @param last the last block info
     * @param fileId the id uniquely identifying a file
     *
     * @return true if all file blocks are minimally replicated or false otherwise
     *
     * @throws AccessControlException If access is denied
     * @throws FileNotFoundException If file <code>src</code> is not found
     * @throws SafeModeException create not allowed in safemode
     * @throws UnresolvedLinkException If <code>src</code> contains a symlink
     * @throws IOException If an I/O error occurred
     */
    @Idempotent
    public boolean complete(String src, String clientName,
                            ExtendedBlock last, long fileId)
            throws AccessControlException, FileNotFoundException, SafeModeException,
            UnresolvedLinkException, IOException;

    /**
     * The client wants to report corrupted blocks (blocks with specified
     * locations on datanodes).
     * @param blocks Array of located blocks to report
     */
    @Idempotent
    public void reportBadBlocks(LocatedBlock[] blocks) throws IOException;

    ///////////////////////////////////////
    // Namespace management
    ///////////////////////////////////////

    /**
     * Rename an item in the file system namespace.
     * @param src existing file or directory name.
     * @param dst new name.
     * @return true if successful, or false if the old name does not exist
     * or if the new name already belongs to the namespace.
     *
     * @throws SnapshotAccessControlException if path is in RO snapshot
     * @throws IOException an I/O error occurred
     */
    @AtMostOnce
    public boolean rename(String src, String dst)
            throws UnresolvedLinkException, SnapshotAccessControlException, IOException;

    /**
     * Moves blocks from srcs to trg and delete srcs
     *
     * @param trg existing file
     * @param srcs - list of existing files (same block size, same replication)
     * @throws IOException if some arguments are invalid
     * @throws UnresolvedLinkException if <code>trg</code> or <code>srcs</code>
     *           contains a symlink
     * @throws SnapshotAccessControlException if path is in RO snapshot
     */
    @AtMostOnce
    public void concat(String trg, String[] srcs)
            throws IOException, UnresolvedLinkException, SnapshotAccessControlException;

    /**
     * Rename src to dst.
     * <ul>
     * <li>Fails if src is a file and dst is a directory.
     * <li>Fails if src is a directory and dst is a file.
     * <li>Fails if the parent of dst does not exist or is a file.
     * </ul>
     * <p>
     * Without OVERWRITE option, rename fails if the dst already exists.
     * With OVERWRITE option, rename overwrites the dst, if it is a file
     * or an empty directory. Rename fails if dst is a non-empty directory.
     * <p>
     * This implementation of rename is atomic.
     * <p>
     * @param src existing file or directory name.
     * @param dst new name.
     * @param options Rename options
     *
     * @throws AccessControlException If access is denied
     * @throws DSQuotaExceededException If rename violates disk space
     *           quota restriction
     * @throws FileAlreadyExistsException If <code>dst</code> already exists and
     *           <code>options</options> has {@link Rename#OVERWRITE} option
     *           false.
     * @throws FileNotFoundException If <code>src</code> does not exist
     * @throws NSQuotaExceededException If rename violates namespace
     *           quota restriction
     * @throws ParentNotDirectoryException If parent of <code>dst</code>
     *           is not a directory
     * @throws SafeModeException rename not allowed in safemode
     * @throws UnresolvedLinkException If <code>src</code> or
     *           <code>dst</code> contains a symlink
     * @throws SnapshotAccessControlException if path is in RO snapshot
     * @throws IOException If an I/O error occurred
     */
    @AtMostOnce
    public void rename2(String src, String dst, Options.Rename... options)
            throws AccessControlException, DSQuotaExceededException,
            FileAlreadyExistsException, FileNotFoundException,
            NSQuotaExceededException, ParentNotDirectoryException, SafeModeException,
            UnresolvedLinkException, SnapshotAccessControlException, IOException;

    /**
     * Delete the given file or directory from the file system.
     * <p>
     * same as delete but provides a way to avoid accidentally
     * deleting non empty directories programmatically.
     * @param src existing name
     * @param recursive if true deletes a non empty directory recursively,
     * else throws an exception.
     * @return true only if the existing file or directory was actually removed
     * from the file system.
     *
     * @throws AccessControlException If access is denied
     * @throws FileNotFoundException If file <code>src</code> is not found
     * @throws SafeModeException create not allowed in safemode
     * @throws UnresolvedLinkException If <code>src</code> contains a symlink
     * @throws SnapshotAccessControlException if path is in RO snapshot
     * @throws IOException If an I/O error occurred
     */
    @AtMostOnce
    public boolean delete(String src, boolean recursive)
            throws AccessControlException, FileNotFoundException, SafeModeException,
            UnresolvedLinkException, SnapshotAccessControlException, IOException;

    /**
     * Create a directory (or hierarchy of directories) with the given
     * name and permission.
     *
     * @param src The path of the directory being created
     * @param masked The masked permission of the directory being created
     * @param createParent create missing parent directory if true
     *
     * @return True if the operation success.
     *
     * @throws AccessControlException If access is denied
     * @throws FileAlreadyExistsException If <code>src</code> already exists
     * @throws FileNotFoundException If parent of <code>src</code> does not exist
     *           and <code>createParent</code> is false
     * @throws NSQuotaExceededException If file creation violates quota restriction
     * @throws ParentNotDirectoryException If parent of <code>src</code>
     *           is not a directory
     * @throws SafeModeException create not allowed in safemode
     * @throws UnresolvedLinkException If <code>src</code> contains a symlink
     * @throws SnapshotAccessControlException if path is in RO snapshot
     * @throws IOException If an I/O error occurred.
     *
     * RunTimeExceptions:
     * @throws InvalidPathException If <code>src</code> is invalid
     */
    @Idempotent
    public boolean mkdirs(String src, FsPermission masked, boolean createParent)
            throws AccessControlException, FileAlreadyExistsException,
            FileNotFoundException, NSQuotaExceededException,
            ParentNotDirectoryException, SafeModeException, UnresolvedLinkException,
            SnapshotAccessControlException, IOException;

    /**
     * Get a partial listing of the indicated directory
     *
     * @param src the directory name
     * @param startAfter the name to start listing after encoded in java UTF8
     * @param needLocation if the FileStatus should contain block locations
     *
     * @return a partial listing starting after startAfter
     *
     * @throws AccessControlException permission denied
     * @throws FileNotFoundException file <code>src</code> is not found
     * @throws UnresolvedLinkException If <code>src</code> contains a symlink
     * @throws IOException If an I/O error occurred
     */
    @Idempotent
    public DirectoryListing getListing(String src,
                                       byte[] startAfter,
                                       boolean needLocation)
            throws AccessControlException, FileNotFoundException,
            UnresolvedLinkException, IOException;

    /**
     * Get listing of all the snapshottable directories
     *
     * @return Information about all the current snapshottable directory
     * @throws IOException If an I/O error occurred
     */
    @Idempotent
    public SnapshottableDirectoryStatus[] getSnapshottableDirListing()
            throws IOException;

    ///////////////////////////////////////
    // System issues and management
    ///////////////////////////////////////

    /**
     * Client programs can cause stateful changes in the NameNode
     * that affect other clients.  A client may obtain a file and
     * neither abandon nor complete it.  A client might hold a series
     * of locks that prevent other clients from proceeding.
     * Clearly, it would be bad if a client held a bunch of locks
     * that it never gave up.  This can happen easily if the client
     * dies unexpectedly.
     * <p>
     * So, the NameNode will revoke the locks and live file-creates
     * for clients that it thinks have died.  A client tells the
     * NameNode that it is still alive by periodically calling
     * renewLease().  If a certain amount of time passes since
     * the last call to renewLease(), the NameNode assumes the
     * client has died.
     *
     * @throws AccessControlException permission denied
     * @throws IOException If an I/O error occurred
     */
    @Idempotent
    public void renewLease(String clientName) throws AccessControlException,
            IOException;

    /**
     * Start lease recovery.
     * Lightweight NameNode operation to trigger lease recovery
     *
     * @param src path of the file to start lease recovery
     * @param clientName name of the current client
     * @return true if the file is already closed
     * @throws IOException
     */
    @Idempotent
    public boolean recoverLease(String src, String clientName) throws IOException;

    public int GET_STATS_CAPACITY_IDX = 0;
    public int GET_STATS_USED_IDX = 1;
    public int GET_STATS_REMAINING_IDX = 2;
    public int GET_STATS_UNDER_REPLICATED_IDX = 3;
    public int GET_STATS_CORRUPT_BLOCKS_IDX = 4;
    public int GET_STATS_MISSING_BLOCKS_IDX = 5;

    /**
     * Get a set of statistics about the filesystem.
     * Right now, only seven values are returned.
     * <ul>
     * <li> [0] contains the total storage capacity of the system, in bytes.</li>
     * <li> [1] contains the total used space of the system, in bytes.</li>
     * <li> [2] contains the available storage of the system, in bytes.</li>
     * <li> [3] contains number of under replicated blocks in the system.</li>
     * <li> [4] contains number of blocks with a corrupt replica. </li>
     * <li> [5] contains number of blocks without any good replicas left. </li>
     * <li> [6] contains the total used space of the block pool. </li>
     * </ul>
     * Use public constants like {@link #GET_STATS_CAPACITY_IDX} in place of
     * actual numbers to index into the array.
     */
    @Idempotent
    public long[] getStats() throws IOException;

    /**
     * Get a report on the system's current datanodes.
     * One DatanodeInfo object is returned for each DataNode.
     * Return live datanodes if type is LIVE; dead datanodes if type is DEAD;
     * otherwise all datanodes if type is ALL.
     */
    @Idempotent
    public DatanodeInfo[] getDatanodeReport(HdfsConstants.DatanodeReportType type)
            throws IOException;

    /**
     * Get a report on the current datanode storages.
     */
    @Idempotent
    public DatanodeStorageReport[] getDatanodeStorageReport(
            HdfsConstants.DatanodeReportType type) throws IOException;

    /**
     * Get the block size for the given file.
     * @param filename The name of the file
     * @return The number of bytes in each block
     * @throws IOException
     * @throws UnresolvedLinkException if the path contains a symlink.
     */
    @Idempotent
    public long getPreferredBlockSize(String filename)
            throws IOException, UnresolvedLinkException;

    /**
     * Enter, leave or get safe mode.
     * <p>
     * Safe mode is a name node state when it
     * <ol><li>does not accept changes to name space (read-only), and</li>
     * <li>does not replicate or delete blocks.</li></ol>
     *
     * <p>
     * Safe mode is entered automatically at name node startup.
     * Safe mode can also be entered manually using
     * {@link #setSafeMode(HdfsConstants.SafeModeAction, boolean) setSafeMode(SafeModeAction.SAFEMODE_ENTER,false)}.
     * <p>
     * At startup the name node accepts data node reports collecting
     * information about block locations.
     * In order to leave safe mode it needs to collect a configurable
     * percentage called threshold of blocks, which satisfy the minimal
     * replication condition.
     * The minimal replication condition is that each block must have at least
     * <tt>dfs.namenode.replication.min</tt> replicas.
     * When the threshold is reached the name node extends safe mode
     * for a configurable amount of time
     * to let the remaining data nodes to check in before it
     * will start replicating missing blocks.
     * Then the name node leaves safe mode.
     * <p>
     * If safe mode is turned on manually using
     * {@link #setSafeMode(HdfsConstants.SafeModeAction, boolean) setSafeMode(SafeModeAction.SAFEMODE_ENTER,false)}
     * then the name node stays in safe mode until it is manually turned off
     * using {@link #setSafeMode(HdfsConstants.SafeModeAction, boolean) setSafeMode(SafeModeAction.SAFEMODE_LEAVE,false)}.
     * Current state of the name node can be verified using
     * {@link #setSafeMode(HdfsConstants.SafeModeAction, boolean) setSafeMode(SafeModeAction.SAFEMODE_GET,false)}
     * <h4>Configuration parameters:</h4>
     * <tt>dfs.safemode.threshold.pct</tt> is the threshold parameter.<br>
     * <tt>dfs.safemode.extension</tt> is the safe mode extension parameter.<br>
     * <tt>dfs.namenode.replication.min</tt> is the minimal replication parameter.
     *
     * <h4>Special cases:</h4>
     * The name node does not enter safe mode at startup if the threshold is
     * set to 0 or if the name space is empty.<br>
     * If the threshold is set to 1 then all blocks need to have at least
     * minimal replication.<br>
     * If the threshold value is greater than 1 then the name node will not be
     * able to turn off safe mode automatically.<br>
     * Safe mode can always be turned off manually.
     *
     * @param action  <ul> <li>0 leave safe mode;</li>
     *                <li>1 enter safe mode;</li>
     *                <li>2 get safe mode state.</li></ul>
     * @param isChecked If true then action will be done only in ActiveNN.
     *
     * @return <ul><li>0 if the safe mode is OFF or</li>
     *         <li>1 if the safe mode is ON.</li></ul>
     *
     * @throws IOException
     */
    @Idempotent
    public boolean setSafeMode(HdfsConstants.SafeModeAction action, boolean isChecked)
            throws IOException;

    /**
     * Save namespace image.
     * <p>
     * Saves current namespace into storage directories and reset edits log.
     * Requires superuser privilege and safe mode.
     *
     * @throws AccessControlException if the superuser privilege is violated.
     * @throws IOException if image creation failed.
     */
    @AtMostOnce
    public void saveNamespace() throws AccessControlException, IOException;


    /**
     * Roll the edit log.
     * Requires superuser privileges.
     *
     * @throws AccessControlException if the superuser privilege is violated
     * @throws IOException if log roll fails
     * @return the txid of the new segment
     */
    @Idempotent
    public long rollEdits() throws AccessControlException, IOException;

    /**
     * Enable/Disable restore failed storage.
     * <p>
     * sets flag to enable restore of failed storage replicas
     *
     * @throws AccessControlException if the superuser privilege is violated.
     */
    @Idempotent
    public boolean restoreFailedStorage(String arg)
            throws AccessControlException, IOException;

    /**
     * Tells the namenode to reread the hosts and exclude files.
     * @throws IOException
     */
    @Idempotent
    public void refreshNodes() throws IOException;

    /**
     * Finalize previous upgrade.
     * Remove file system state saved during the upgrade.
     * The upgrade will become irreversible.
     *
     * @throws IOException
     */
    @Idempotent
    public void finalizeUpgrade() throws IOException;

    /**
     * Rolling upgrade operations.
     * @param action either query, start or finailze.
     * @return rolling upgrade information.
     */
    @Idempotent
    public RollingUpgradeInfo rollingUpgrade(RollingUpgradeAction action)
            throws IOException;

    /**
     * @return CorruptFileBlocks, containing a list of corrupt files (with
     *         duplicates if there is more than one corrupt block in a file)
     *         and a cookie
     * @throws IOException
     *
     * Each call returns a subset of the corrupt files in the system. To obtain
     * all corrupt files, call this method repeatedly and each time pass in the
     * cookie returned from the previous call.
     */
    @Idempotent
    public CorruptFileBlocks listCorruptFileBlocks(String path, String cookie)
            throws IOException;

    /**
     * Dumps namenode data structures into specified file. If the file
     * already exists, then append.
     *
     * @throws IOException
     */
    @Idempotent
    public void metaSave(String filename) throws IOException;

    /**
     * Tell all datanodes to use a new, non-persistent bandwidth value for
     * dfs.balance.bandwidthPerSec.
     *
     * @param bandwidth Blanacer bandwidth in bytes per second for this datanode.
     * @throws IOException
     */
    @Idempotent
    public void setBalancerBandwidth(long bandwidth) throws IOException;

    /**
     * Get the file info for a specific file or directory.
     * @param src The string representation of the path to the file
     *
     * @return object containing information regarding the file
     *         or null if file not found
     * @throws AccessControlException permission denied
     * @throws FileNotFoundException file <code>src</code> is not found
     * @throws UnresolvedLinkException if the path contains a symlink.
     * @throws IOException If an I/O error occurred
     */
    @Idempotent
    public HdfsFileStatus getFileInfo(String src) throws AccessControlException,
            FileNotFoundException, UnresolvedLinkException, IOException;

    /**
     * Get the close status of a file
     * @param src The string representation of the path to the file
     *
     * @return return true if file is closed
     * @throws AccessControlException permission denied
     * @throws FileNotFoundException file <code>src</code> is not found
     * @throws UnresolvedLinkException if the path contains a symlink.
     * @throws IOException If an I/O error occurred
     */
    @Idempotent
    public boolean isFileClosed(String src) throws AccessControlException,
            FileNotFoundException, UnresolvedLinkException, IOException;

    /**
     * Get the file info for a specific file or directory. If the path
     * refers to a symlink then the FileStatus of the symlink is returned.
     * @param src The string representation of the path to the file
     *
     * @return object containing information regarding the file
     *         or null if file not found
     *
     * @throws AccessControlException permission denied
     * @throws UnresolvedLinkException if <code>src</code> contains a symlink
     * @throws IOException If an I/O error occurred
     */
    @Idempotent
    public HdfsFileStatus getFileLinkInfo(String src)
            throws AccessControlException, UnresolvedLinkException, IOException;

    /**
     * Get {@link ContentSummary} rooted at the specified directory.
     * @param path The string representation of the path
     *
     * @throws AccessControlException permission denied
     * @throws FileNotFoundException file <code>path</code> is not found
     * @throws UnresolvedLinkException if <code>path</code> contains a symlink.
     * @throws IOException If an I/O error occurred
     */
    @Idempotent
    public ContentSummary getContentSummary(String path)
            throws AccessControlException, FileNotFoundException,
            UnresolvedLinkException, IOException;

    /**
     * Set the quota for a directory.
     * @param path  The string representation of the path to the directory
     * @param namespaceQuota Limit on the number of names in the tree rooted
     *                       at the directory
     * @param diskspaceQuota Limit on disk space occupied all the files under
     *                       this directory.
     * <br><br>
     *
     * The quota can have three types of values : (1) 0 or more will set
     * the quota to that value, (2) {@link HdfsConstants#QUOTA_DONT_SET}  implies
     * the quota will not be changed, and (3) {@link HdfsConstants#QUOTA_RESET}
     * implies the quota will be reset. Any other value is a runtime error.
     *
     * @throws AccessControlException permission denied
     * @throws FileNotFoundException file <code>path</code> is not found
     * @throws QuotaExceededException if the directory size
     *           is greater than the given quota
     * @throws UnresolvedLinkException if the <code>path</code> contains a symlink.
     * @throws SnapshotAccessControlException if path is in RO snapshot
     * @throws IOException If an I/O error occurred
     */
    @Idempotent
    public void setQuota(String path, long namespaceQuota, long diskspaceQuota)
            throws AccessControlException, FileNotFoundException,
            UnresolvedLinkException, SnapshotAccessControlException, IOException;

    /**
     * Write all metadata for this file into persistent storage.
     * The file must be currently open for writing.
     * @param src The string representation of the path
     * @param inodeId The inode ID, or GRANDFATHER_INODE_ID if the client is
     *                too old to support fsync with inode IDs.
     * @param client The string representation of the client
     * @param lastBlockLength The length of the last block (under construction)
     *                        to be reported to NameNode
     * @throws AccessControlException permission denied
     * @throws FileNotFoundException file <code>src</code> is not found
     * @throws UnresolvedLinkException if <code>src</code> contains a symlink.
     * @throws IOException If an I/O error occurred
     */
    @Idempotent
    public void fsync(String src, long inodeId, String client,
                      long lastBlockLength)
            throws AccessControlException, FileNotFoundException,
            UnresolvedLinkException, IOException;

    /**
     * Sets the modification and access time of the file to the specified time.
     * @param src The string representation of the path
     * @param mtime The number of milliseconds since Jan 1, 1970.
     *              Setting mtime to -1 means that modification time should not be set
     *              by this call.
     * @param atime The number of milliseconds since Jan 1, 1970.
     *              Setting atime to -1 means that access time should not be set
     *              by this call.
     *
     * @throws AccessControlException permission denied
     * @throws FileNotFoundException file <code>src</code> is not found
     * @throws UnresolvedLinkException if <code>src</code> contains a symlink.
     * @throws SnapshotAccessControlException if path is in RO snapshot
     * @throws IOException If an I/O error occurred
     */
    @Idempotent
    public void setTimes(String src, long mtime, long atime)
            throws AccessControlException, FileNotFoundException,
            UnresolvedLinkException, SnapshotAccessControlException, IOException;

    /**
     * Create symlink to a file or directory.
     * @param target The path of the destination that the
     *               link points to.
     * @param link The path of the link being created.
     * @param dirPerm permissions to use when creating parent directories
     * @param createParent - if true then missing parent dirs are created
     *                       if false then parent must exist
     *
     * @throws AccessControlException permission denied
     * @throws FileAlreadyExistsException If file <code>link</code> already exists
     * @throws FileNotFoundException If parent of <code>link</code> does not exist
     *           and <code>createParent</code> is false
     * @throws ParentNotDirectoryException If parent of <code>link</code> is not a
     *           directory.
     * @throws UnresolvedLinkException if <code>link</target> contains a symlink.
     * @throws SnapshotAccessControlException if path is in RO snapshot
     * @throws IOException If an I/O error occurred
     */
    @AtMostOnce
    public void createSymlink(String target, String link, FsPermission dirPerm,
                              boolean createParent) throws AccessControlException,
            FileAlreadyExistsException, FileNotFoundException,
            ParentNotDirectoryException, SafeModeException, UnresolvedLinkException,
            SnapshotAccessControlException, IOException;

    /**
     * Return the target of the given symlink. If there is an intermediate
     * symlink in the path (ie a symlink leading up to the final path component)
     * then the given path is returned with this symlink resolved.
     *
     * @param path The path with a link that needs resolution.
     * @return The path after resolving the first symbolic link in the path.
     * @throws AccessControlException permission denied
     * @throws FileNotFoundException If <code>path</code> does not exist
     * @throws IOException If the given path does not refer to a symlink
     *           or an I/O error occurred
     */
    @Idempotent
    public String getLinkTarget(String path) throws AccessControlException,
            FileNotFoundException, IOException;

    /**
     * Get a new generation stamp together with an access token for
     * a block under construction
     *
     * This method is called only when a client needs to recover a failed
     * pipeline or set up a pipeline for appending to a block.
     *
     * @param block a block
     * @param clientName the name of the client
     * @return a located block with a new generation stamp and an access token
     * @throws IOException if any error occurs
     */
    @Idempotent
    public LocatedBlock updateBlockForPipeline(ExtendedBlock block,
                                               String clientName) throws IOException;

    /**
     * Update a pipeline for a block under construction
     *
     * @param clientName the name of the client
     * @param oldBlock the old block
     * @param newBlock the new block containing new generation stamp and length
     * @param newNodes datanodes in the pipeline
     * @throws IOException if any error occurs
     */
    @AtMostOnce
    public void updatePipeline(String clientName, ExtendedBlock oldBlock,
                               ExtendedBlock newBlock, DatanodeID[] newNodes, String[] newStorageIDs)
            throws IOException;

    /**
     * Get a valid Delegation Token.
     *
     * @param renewer the designated renewer for the token
     * @return Token<DelegationTokenIdentifier>
     * @throws IOException
     */
    @Idempotent
    public Token<DelegationTokenIdentifier> getDelegationToken(Text renewer)
            throws IOException;

    /**
     * Renew an existing delegation token.
     *
     * @param token delegation token obtained earlier
     * @return the new expiration time
     * @throws IOException
     */
    @Idempotent
    public long renewDelegationToken(Token<DelegationTokenIdentifier> token)
            throws IOException;

    /**
     * Cancel an existing delegation token.
     *
     * @param token delegation token
     * @throws IOException
     */
    @Idempotent
    public void cancelDelegationToken(Token<DelegationTokenIdentifier> token)
            throws IOException;

    /**
     * @return encryption key so a client can encrypt data sent via the
     *         DataTransferProtocol to/from DataNodes.
     * @throws IOException
     */
    @Idempotent
    public DataEncryptionKey getDataEncryptionKey() throws IOException;

    /**
     * Create a snapshot
     * @param snapshotRoot the path that is being snapshotted
     * @param snapshotName name of the snapshot created
     * @return the snapshot path.
     * @throws IOException
     */
    @AtMostOnce
    public String createSnapshot(String snapshotRoot, String snapshotName)
            throws IOException;

    /**
     * Delete a specific snapshot of a snapshottable directory
     * @param snapshotRoot  The snapshottable directory
     * @param snapshotName Name of the snapshot for the snapshottable directory
     * @throws IOException
     */
    @AtMostOnce
    public void deleteSnapshot(String snapshotRoot, String snapshotName)
            throws IOException;

    /**
     * Rename a snapshot
     * @param snapshotRoot the directory path where the snapshot was taken
     * @param snapshotOldName old name of the snapshot
     * @param snapshotNewName new name of the snapshot
     * @throws IOException
     */
    @AtMostOnce
    public void renameSnapshot(String snapshotRoot, String snapshotOldName,
                               String snapshotNewName) throws IOException;

    /**
     * Allow snapshot on a directory.
     * @param snapshotRoot the directory to be snapped
     * @throws IOException on error
     */
    @Idempotent
    public void allowSnapshot(String snapshotRoot)
            throws IOException;

    /**
     * Disallow snapshot on a directory.
     * @param snapshotRoot the directory to disallow snapshot
     * @throws IOException on error
     */
    @Idempotent
    public void disallowSnapshot(String snapshotRoot)
            throws IOException;

    /**
     * Get the difference between two snapshots, or between a snapshot and the
     * current tree of a directory.
     *
     * @param snapshotRoot
     *          full path of the directory where snapshots are taken
     * @param fromSnapshot
     *          snapshot name of the from point. Null indicates the current
     *          tree
     * @param toSnapshot
     *          snapshot name of the to point. Null indicates the current
     *          tree.
     * @return The difference report represented as a {@link SnapshotDiffReport}.
     * @throws IOException on error
     */
    @Idempotent
    public SnapshotDiffReport getSnapshotDiffReport(String snapshotRoot,
                                                    String fromSnapshot, String toSnapshot) throws IOException;

    /**
     * Add a CacheDirective to the CacheManager.
     *
     * @param directive A CacheDirectiveInfo to be added
     * @param flags {@link CacheFlag}s to use for this operation.
     * @return A CacheDirectiveInfo associated with the added directive
     * @throws IOException if the directive could not be added
     */
    @AtMostOnce
    public long addCacheDirective(CacheDirectiveInfo directive,
                                  EnumSet<CacheFlag> flags) throws IOException;

    /**
     * Modify a CacheDirective in the CacheManager.
     *
     * @param flags {@link CacheFlag}s to use for this operation.
     * @throws IOException if the directive could not be modified
     */
    @AtMostOnce
    public void modifyCacheDirective(CacheDirectiveInfo directive,
                                     EnumSet<CacheFlag> flags) throws IOException;

    /**
     * Remove a CacheDirectiveInfo from the CacheManager.
     *
     * @param id of a CacheDirectiveInfo
     * @throws IOException if the cache directive could not be removed
     */
    @AtMostOnce
    public void removeCacheDirective(long id) throws IOException;

    /**
     * List the set of cached paths of a cache pool. Incrementally fetches results
     * from the server.
     *
     * @param prevId The last listed entry ID, or -1 if this is the first call to
     *               listCacheDirectives.
     * @param filter Parameters to use to filter the list results,
     *               or null to display all directives visible to us.
     * @return A batch of CacheDirectiveEntry objects.
     */
    @Idempotent
    public BatchedEntries<CacheDirectiveEntry> listCacheDirectives(
            long prevId, CacheDirectiveInfo filter) throws IOException;

    /**
     * Add a new cache pool.
     *
     * @param info Description of the new cache pool
     * @throws IOException If the request could not be completed.
     * 创建一个缓存池
     */
    @AtMostOnce
    public void addCachePool(CachePoolInfo info) throws IOException;

    /**
     * Modify an existing cache pool.
     *
     * @param req
     *          The request to modify a cache pool.
     * @throws IOException
     *          If the request could not be completed.
     */
    @AtMostOnce
    public void modifyCachePool(CachePoolInfo req) throws IOException;

    /**
     * Remove a cache pool.
     *
     * @param pool name of the cache pool to remove.
     * @throws IOException if the cache pool did not exist, or could not be
     *           removed.
     */
    @AtMostOnce
    public void removeCachePool(String pool) throws IOException;

    /**
     * List the set of cache pools. Incrementally fetches results from the server.
     *
     * @param prevPool name of the last pool listed, or the empty string if this is
     *          the first invocation of listCachePools
     * @return A batch of CachePoolEntry objects.
     */
    @Idempotent
    public BatchedEntries<CachePoolEntry> listCachePools(String prevPool)
            throws IOException;

    /**
     * Modifies ACL entries of files and directories.  This method can add new ACL
     * entries or modify the permissions on existing ACL entries.  All existing
     * ACL entries that are not specified in this call are retained without
     * changes.  (Modifications are merged into the current ACL.)
     */
    @Idempotent
    public void modifyAclEntries(String src, List<AclEntry> aclSpec)
            throws IOException;

    /**
     * Removes ACL entries from files and directories.  Other ACL entries are
     * retained.
     */
    @Idempotent
    public void removeAclEntries(String src, List<AclEntry> aclSpec)
            throws IOException;

    /**
     * Removes all default ACL entries from files and directories.
     */
    @Idempotent
    public void removeDefaultAcl(String src) throws IOException;

    /**
     * Removes all but the base ACL entries of files and directories.  The entries
     * for user, group, and others are retained for compatibility with permission
     * bits.
     */
    @Idempotent
    public void removeAcl(String src) throws IOException;

    /**
     * Fully replaces ACL of files and directories, discarding all existing
     * entries.
     */
    @Idempotent
    public void setAcl(String src, List<AclEntry> aclSpec) throws IOException;

    /**
     * Gets the ACLs of files and directories.
     */
    @Idempotent
    public AclStatus getAclStatus(String src) throws IOException;

    /**
     * Create an encryption zone
     */
    @AtMostOnce
    public void createEncryptionZone(String src, String keyName)
            throws IOException;

    /**
     * Get the encryption zone for a path.
     */
    @Idempotent
    public EncryptionZone getEZForPath(String src)
            throws IOException;

    /**
     * Used to implement cursor-based batched listing of {@EncryptionZone}s.
     *
     * @param prevId ID of the last item in the previous batch. If there is no
     *               previous batch, a negative value can be used.
     * @return Batch of encryption zones.
     */
    @Idempotent
    public BatchedEntries<EncryptionZone> listEncryptionZones(
            long prevId) throws IOException;

    /**
     * Set xattr of a file or directory.
     * The name must be prefixed with the namespace followed by ".". For example,
     * "user.attr".
     * <p/>
     * Refer to the HDFS extended attributes user documentation for details.
     *
     * @param src file or directory
     * @param xAttr <code>XAttr</code> to set
     * @param flag set flag
     * @throws IOException
     */
    @AtMostOnce
    public void setXAttr(String src, XAttr xAttr, EnumSet<XAttrSetFlag> flag)
            throws IOException;

    /**
     * Get xattrs of a file or directory. Values in xAttrs parameter are ignored.
     * If xAttrs is null or empty, this is the same as getting all xattrs of the
     * file or directory.  Only those xattrs for which the logged-in user has
     * permissions to view are returned.
     * <p/>
     * Refer to the HDFS extended attributes user documentation for details.
     *
     * @param src file or directory
     * @param xAttrs xAttrs to get
     * @return List<XAttr> <code>XAttr</code> list
     * @throws IOException
     */
    @Idempotent
    public List<XAttr> getXAttrs(String src, List<XAttr> xAttrs)
            throws IOException;

    /**
     * List the xattrs names for a file or directory.
     * Only the xattr names for which the logged in user has the permissions to
     * access will be returned.
     * <p/>
     * Refer to the HDFS extended attributes user documentation for details.
     *
     * @param src file or directory
     * @return List<XAttr> <code>XAttr</code> list
     * @throws IOException
     */
    @Idempotent
    public List<XAttr> listXAttrs(String src)
            throws IOException;

    /**
     * Remove xattr of a file or directory.Value in xAttr parameter is ignored.
     * The name must be prefixed with the namespace followed by ".". For example,
     * "user.attr".
     * <p/>
     * Refer to the HDFS extended attributes user documentation for details.
     *
     * @param src file or directory
     * @param xAttr <code>XAttr</code> to remove
     * @throws IOException
     */
    @AtMostOnce
    public void removeXAttr(String src, XAttr xAttr) throws IOException;

    /**
     * Checks if the user can access a path.  The mode specifies which access
     * checks to perform.  If the requested permissions are granted, then the
     * method returns normally.  If access is denied, then the method throws an
     * {@link AccessControlException}.
     * In general, applications should avoid using this method, due to the risk of
     * time-of-check/time-of-use race conditions.  The permissions on a file may
     * change immediately after the access call returns.
     *
     * @param path Path to check
     * @param mode type of access to check
     * @throws AccessControlException if access is denied
     * @throws FileNotFoundException if the path does not exist
     * @throws IOException see specific implementation
     */
    @Idempotent
    public void checkAccess(String path, FsAction mode) throws IOException;

    /**
     * Get the highest txid the NameNode knows has been written to the edit
     * log, or -1 if the NameNode's edit log is not yet open for write. Used as
     * the starting point for the inotify event stream.
     */
    @Idempotent
    public long getCurrentEditLogTxid() throws IOException;

    /**
     * Get an ordered list of batches of events corresponding to the edit log
     * transactions for txids equal to or greater than txid.
     */
    @Idempotent
    public EventBatchList getEditsFromTxid(long txid) throws IOException;
}
